No, I'm saying that the problem you worry about doesn't exist. The problem -- as you point out -- with 2 -> 3 was that supporting both versions was very diffic

No, I'm saying that the problem you worry about doesn't exist. The problem -- as you point out -- with 2 -> 3 was that supporting both versions was very difficult. Because Python 2 couldn't run Python 3 code (and vice versa). And thus libraries existed in awkward states for years. But GIL can run no-GIL code. Supporting both is no harder than supporting one of those options (the no-GIL one).